Misfit strain phase diagrams of epitaxial PMN–PT films

Abstract

Misfit strain-temperature phase diagrams of three compositions of (001) pseudocubic (1 À x)ÁPb (Mg l/3 Nb 2/3 )O 3 À xÁPbTiO 3 (PMN-PT) thin films are computed using a phenomenological model. Two (x ¼ 0.30, 0.42) are located near the morphotropic phase boundary (MPB) of bulk PMN-PT at room temperature (RT) and one (x ¼ 0.70) is located far from the MPB. The results show that it is possible to stabilize an adaptive monoclinic phase over a wide range of misfit strains. At RT, the stability region of this phase is much larger for PMN-PT compared to barium strontium titanate and lead zirconate titanate films. V C 2015 AIP Publishing LLC.Piezoelectric ceramics have been widely used in the conversion of electrical energy to mechanical energy and vice versa. The potential of these materials for deployment in applications such as transducers, 1 sensors, and actuators, 2 and acoustic resonators in radio frequency (RF) telecommunication systems 3 has been a driving force for extensive research to discover, understand, and implement piezoelectric material systems in such devices. Piezoelectric response is largest in ferroelectric (FE) materials. 4 The most prominent example is lead zirconate titanate (PbZr x Ti 1 À x O 3 , PZT) which has been the material of choice in many applications. Lead-free FE oxides, such as BaTiO 3 5 and BiFeO 3 , 6,7 also display a large piezoelectric response ($200 and $50 pm/V, respectively), although their magnitude of the piezoelectric coefficient is smaller than PZT ($500 pm/V). Lead magnesium niobate-lead titanate [(1 À x)ÁPb(Mg l/3 Nb 2/3 )O 3 ÀxÁPbTiO 3 (PMN-PT)] is one of the most important binary lead-based relaxor ferroelectric systems which, in single crystal form, shows superior performance in sensor/actuator applications. 8 Depending on the PT concentration, compositions in the PMN-PT solid solution possess weak remnant polarization and show frequency dispersive dielectric response. 9 Theoretical calculations based on the phenomenological theory show that it is possible to stabilize different phases in epitaxial ferroelectric films that are not accessible in bulk form. 10 The stabilization of these phases arises due to equibiaxial in-plane misfit strains. The initial work of Pertsev et al. and follow-on studies have generated the misfit strain (u m )-temperature (T) phase diagrams for epitaxial thin films of PbTiO 3 , PZT, BaTiO 3 , SrTiO 3 , and Ba 1Àx Sr x TiO 3 (BST), and the dielectric, pyroelectric/electrocaloric, and piezoelectric properties as a function of the misfit strain and temperature have been computed. 11-17 Although monocrystalline PMN-PT compositions located near the morphotropic phase boundary (MPB) exhibit outstanding piezoelectric properties (d 33 > 1500 pC/m and electromechanical coupling factors k 33 > 0.92), 18 the lack of a Landau-Devonshire free energy function hindered the development of u m -T diagrams for PMN-PT materials. Such diagrams would particularly be important in the development of new generation of electrically switchable and tunable surface and bu...

A thermodynamic potential for barium zirconate titanate solid solutions

“…Thermodynamic analysis based on phenomenological Landau-Devonshire theory is a powerful method for the theoretical investigation of ferroelectric materials. 3,7,[24][25][26][27][28][29][30][31][32][33][34][35] In order to implement thermodynamic analysis, the thermodynamic potential of a particular ferroelectric system should be established first. Haun et al have established the thermodynamic potential for lead zirconate titanate (PZT) solid solution based on its phase structures and electromechanical properties in single crystals and bulk ceramics.…”

Electric-field-induced phase transition and electrocaloric effect in PMN-PT

“…[24,28] The mechanism of the EC enhancement near the MPB region is associated with an easy path for polarization rotation. First-principles calculations, [30][31][32][33][34] atomic-level MD simulations [35][36][37][38], Monte-Carlo simulations [39] and phenomenological Landau theories [40,41] have been used to study the electric field-induced phase transition in ferroelectrics. Among these methods, MD simulations with shell models fitted to firstprinciples calculations are sufficient for predicting the behavior of pure compounds and solid solutions.…”

MC Type Phase Structure and Temperature‐Induced MC‐C Transition in the As‐Grown PMN‐0.36PT Single Crystal

“…The qualitative behavior of the free energy and its effect on the polarization rotation behavior is then more significant than in the BaTiO 3 crystals. The vanishing polarization anisotropy around the MPB region then leads to a much more favorable consequence: extremely small energy barrier for polarization rotation among the <001> , <011>, and <111> directions . This is the fundamental reason that the MPB PMN‐ x PTs are prone to complex and multiphase microstructures with ultrahigh piezoelectric and dielectric responses.…”